The conventional measuring instrument for measuring voltage, current, average power and power factor generally utilize analog circuits for counting. Disadvantages of the analog circuit counting process are its low accuracy, poor stability, and high error rate. It is inevitable that the error varies with the voltage and waveform of electric current. For example, when a current signal having a sine wave character passes through a SCR circuit or other type of rectifier circuit, its output waveform will be distorted into a non-standard sine wave. Although there are digital power meters being developed for power measuring, none of them is satisfactory for measuring voltage true root-mean-square, current true root-mean-square, average power and power factor. The present invention provides a digitizing power meter which is accurate in use and which can eliminate the above problems. Advantages of a digitizing power meter in accordance with the present invention include:
1. High accuracy in measuring voltage root-mean-square, current root-mean-square, average power and power factor; (i.e. Accuracy) PA1 2. Capability for measuring voltage and current signal of any waveform; PA1 3. Capability for measuring DC signal Bandwidth up to 100 KHZ, and monitoring its measuring operation by means of a voltage monitor and current monitor; PA1 4. Simple structure, no phase error, and measuring range selectability; PA1 5. Easy to operate through keyboard control; with automatic correction by a microprocessor; PA1 6. High accuracy operation through digital integration, free from influence of temperature and environment; PA1 7. IEEE-488 Interface for connection to other equipment.
An embodiment of the present invention utilizes a voltage divider circuit, a current divider circuit and a voltage/current isolating amplifier, instead of the voltage transformer and current transformer that are used in conventional power meters. The measuring instrument of this invention is capable of measuring the power of any low frequency signal and various DC signals. Because of the advantages of simple structure, no phase error and variable measuring range, the present invention provides a convenient power measuring operation.